Finding and Fixing Home Air Leaks

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A blower door is installed in one of a home's entries so that the building can be pressurized to find air leaks.
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Instrumentation on the blower door allows the pressure to be adjusted inside the building.
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The energy auditor searches out air leaks by checking likely spots with a smoke pencil.

When the temperature dropped and heating costs
jumped — two signs of fall — you decided to improve
the thermal performance of your home. So to button up your
house, you headed down to the hardware store to buy some of
those do-it-yourself weatherization kits that you’d seen
advertised so widely. You picked up storm windows, rolls of
weather stripping and tubes of caulk to seal cracks around
doors and windows.

Yet, although you then spent an entire weekend on your
weatherization project, winter has shown you that your
house is still fairly drafty. There must, you reason, be
other places that are letting the north wind blow in.

Finding the Other Home Air Leaks

According to Carl Ellerbrook, an “energy doctor,” 80 to 90 percent of the home air leaks (called infiltration) in most houses come
from holes that people don’t even know about. The average
dwelling has 10 or so leakage areas, which may account for
as much as 40 percent of the home’s total heating and cooling
requirements, and those window and door kits you installed
only took care of two of them. To really snuggle
up for the winter, you’ve got to find the rest of the gaps
in your dwelling’s shell.

Ellerbrook’s business — through his company, the Sunup
Energy Group Ltd. of Old Snowmass, Colo. — is
finding and sealing the other leaks. To do so, he performs
energy audits using a sophisticated device called a
blower door. This huge fan fits into an exterior
doorway and pressurizes a building to increase the leakage
rate. Then Carl uses a smoke pencil to trace drafts to
their sources. With the blower door and smoke pencil, he
can pinpoint even small leaks.

“Because every house is different,” states Carl, “it’s nice
to use a blower door and smoke pencil to take the guesswork
out of finding leaks.” Still, after several years of
experience with that equipment, Carl has learned where most
of the typical problem areas are in the average home. So
although a competent energy audit is the best way to find
the thermal leaks in your home, checking out Carl’s list of
the 10 worst offenders will go a long way toward keeping
you cozy when the snow flies.

“You’ll find air infiltration anywhere there’s penetration
through the inside or outside shells of a building,” says
Ellerbrook. Make a complete walk-through inspection of your
house, examining the following areas with particular care.
Then seal each leak from the inside of the house.
Weatherization materials will last much longer indoors,
where they’re protected from harsh weather, and moisture
problems within the wall will be avoided.

Bottom Plates

“If you don’t do anything else,” says Carl, “seal all gaps
between the subfloor and the bottom plate.” In new
construction, this can be done by caulking the bottom
plates (the bottom, horizontal boards in walls) as they’re
installed. In existing buildings, however, you’ll have to
seal between the baseboards and the bottom plates.

A polyurethane foam sealant applied to the cracks will fill
any gaps and stop infiltration. This material is
particularly useful for leaks that are large (¼ to 2 inches wide), because it will expand to fill the cavity. When you
use the material, however, be sure to pull carpet back and
move furniture out of the way to avoid spills. It’s also a
good idea to practice a little before you attempt your
first touchy sealing job.

Electric Outlets and Switches

Remove the cover plates from all switches and outlets and
install foam gaskets. These should be readily available at
hardware stores. To get a really tight seal, you can add
plastic socket plugs to unused receptacles.

Outlet and switch covers can actually account for up to 20 percent of your home’s air leaks, and the gaskets cost only about
$1.35 for a package of six. This is one of the least
expensive, easiest sealing jobs you can tackle.

Beam Pockets and Junctions of Dissimilar Materials

Since heat rises, you could be losing a lot of energy
through cracks in the ceiling. Caulk thoroughly around the
edges of beams and anywhere two different materials meet.
Because the dissimilar materials shrink and expand at
different rates, cracks are fairly common.

As long as the gaps aren’t too large, caulk is the best
sealant for visible parts of the ceiling. It can be
smoothed to make the patch job barely discernible.
Ellerbrook recommends Geocel’s elastomeric copolymer caulk
because it’s extremely flexible, but adds that any
siliconized acrylic latex caulk with a 15- to 25-year
warranty will work acceptably. A quality caulk will cost
about $6.00 per tube.

Vanities and Sinks

The holes that are drilled under kitchen and bathroom sinks
for plumbing runs are often oversized to allow for a little
error in layout. The offending gaps are then covered with
flanges and, unfortunately, are seldom sealed. Lift the
flanges on all pipes that pass through the walls or floor
of your home, and seal them with foam.


Gaps between a door and its frame should be sealed with
weather stripping, but the frame itself should be caulked
to prevent leakage around the outside of the door jambs. To
seal the bottoms of doors, use weather-stripping tape and
vinyl door sweeps on all sills. If you have metal doors,
it’s a good idea to pick a product that uses magnetic
weather stripping to provide a tight seal.

Con-Serv, Incorporated makes a garage door insulating cover
that attaches to the inside and adds R-5. The vinyl-faced
fiberglass also helps seal a leaky door. Expect to pay
about $65 for one of these kits.

Window Air Leaks

There are a great many products available for sealing
windows, but the most practical retrofit is to apply heavy
plastic and seal it to the window frame with polyethylene
tape. An equally easy, but slightly less effective,
approach is to use caulking cord, for which you can expect
to pay about $3.00 per roll.

You can also buy kits for sealing windows. The Bede system,
for example, includes a plastic sheet that attaches to
vinyl channels. When the material is heated with a hair
dryer, it draws up “drum tight” for a crystal clear
appearance. This treatment costs about 60 cents per square

While you’re working on your windows, you should also
consider using insulated shades or shutters. Not only will
these increase the R-value of the glazed area, but they’ll
help seal as well.

Air Conditioners and Attic Fans

Fans and air conditioners should be covered with plastic
and sealed with tape or caulk when they’re not in use.
Con-Serv makes an indoor air-conditioner cover that seals,
insulates and reflects heat. Another option is to remove
the unit from the window for the winter and store it in a
sheltered location.


Caulk around the fireplace mantel and sides, using foam
backer rod to fill cracks that are too big for caulking
alone. Stone fireplaces to which drywall abuts are
particularly troublesome. Also, check the fireplace damper
to see that it closes tightly and seals well. (Since you’ll
be using the fireplace during the winter, the only good
remedy for a leaky damper is to replace it.)

Wiring Penetrations

Use a polyurethane sealant around all wires that penetrate
the house walls. It will take a close inspection to find
all of the holes that have been drilled for these items,
but a thorough sealing job will cure a lot of small,
nagging drafts.

Other Holes

You’ll probably be surprised to see how badly the frames of
exhaust vents, recessed lights, registers and trapdoors
seal to the surrounding material. These ill-fitting devices
can let a tremendous amount of air into your home.
Remember, too, that vents — whether they be for
bathroom exhaust fans, your clothes dryer or a range
hood — should have a flap that seals automatically when
the appliance isn’t in use. In addition, if you have
registers that are closed off, install a magnetic seal over
them: Most operable registers leak at a rate of 30 to 40 percent of maximum capacity when closed. (Be aware, however, that
furnaces with burners may overheat if too many registers
are closed.)

These 10 steps will cut energy-wasting air leaks in your
home down to a tolerable level, but the building will
probably still allow enough air to pass through the shell
to keep the indoor environment fresh. In general, only
those buildings that were built to be tight will
need an air-to-air heat exchanger.

Once you’ve stopped the wind from blowing straight through
your house, you can attend to other areas of energy
efficiency. Add insulation (if your dwelling doesn’t
already have an adequate thermal blanket), have your
furnace tuned, replace its air filter, insulate your water
heater’s tank and delivery lines, install water-saving
shower heads and faucets and consider using products such
as insulating pads for your beds, destratification fans to
pull warm air down from the ceiling or a clothes dryer
heat exchanger. By sealing up tight and then nibbling away
at the energy wasters and home air leaks in your household, you can save a
small fortune every winter!

The Energy-Auditing Business

Making house calls as an energy doctor is a profession
with obvious potential. Eighty percent of the housing
that’s available today will still be in use when the year
2000 rolls around, and at least half of those buildings are
veritable energy sieves. It’s hard enough now to pay the
utility bills on an energy eater, and as fuel prices rise,
owners of such dwellings are going to need help!

Carl Ellerbrook says that it takes about $10,000 to get
started in the energy-auditing and weatherization business…that’s enough to cover equipment, materials and
advertising. You’ll need a blower door, a smoke pencil, a
tape measure, a compass, plastic sheets and tape to
perform the energy audit. Then a ladder, a caulking gun, a
drill, a carpet kick tool and common hand tools will be
needed to make the repairs.

You’ll also have to keep a stock of
weatherization supplies on hand. These include polyurethane
foam, caulking, outlet seals and plugs, backer rod, vinyl
door sweeps and storm window kits. An average house of
1,800 square feet could need as many as 50 tubes of caulk,
5 pounds of polyurethane foam and 100 outlet and switch
gaskets. Be sure to keep paper towels, bags and a can of
acetate on hand to clean up spills.

It’s best to work in pairs when weatherizing a house — some jobs just seem to demand at least three hands. Also,
you can expect to put in 30 to 60 person-hours on each
building, so doubling up gets you in and out of a
customer’s home more quickly.

You should find it easy to get people excited about
saving energy if you can convince them that they’ll also be
saving money. Use simple advertisements in newspapers,
fliers and word of mouth to get your message out. Be sure
to let people know that you can offer either a basic energy
audit or complete service, including weatherization.

Your audit should consist of measuring the air changes
per hour of the house (this is done with the blower door),
inspecting the building for problem areas and reporting to
the homeowneron the procedures you recommend (include a
prioritized list of steps to be taken and the savings
possible with each). You should offer other basic energy
conservation materials and services, such as insulation,
water-saving faucets and water heater insulation.

The actual amount you charge will vary greatly
depending on the job. Ellerbrook’s Sunup Energy Group Ltd.
charges 35 to 50 cents per square foot of floor area
for its services. A small weatherization business can grow
rapidly within a few years. Ellerbrook started in 1982 and
has already joined with architect Peter Dobrovolny to form
a full-service residential energy business. Sunup now
offers complete active and passive solar consulting, a
passive solar design and construction service and retail
sales of energy-conserving products, along with home energy
audits and weatherization.

With today’s heightened energy consciousness, the time
is ripe to market conservation.